Known in the state of the art already is the effect of the character of the substrate on the characteristic curve of the thereon located, resistive element. German patents, DE 43 00 084 A1 and DE 195 40 194 C1 indicate, for example, that the characteristic curve of the resistance thermometer has the desired properties, when the thermal coefficient of expansion (TCE), also known as the coefficient of thermal expansion, of the substrate of magnesium titanate lies in the range between 8.5 and 10.5 ppm/K.
Known in the state of the art are temperature measuring devices, in the case of which an electrical, temperature dependent resistance of a resistive element is measured and evaluated. For the evaluation, it is required that the temperature resistance curve, i.e. the relevant characteristic curve of the element, be known.
Known, especially, are resistive elements, which are applied with thin layer techniques onto an electrically insulating substrate. The thin film is composed, as a rule, of platinum or nickel, with or without doping, and the substrate is composed most often of Al2O3.
Known in the state of the art already is the effect of the character of the substrate on the characteristic curve of the thereon located, resistive element. DE 43 00 084 A1 and DE 195 40 194 C1 indicate, for example, that the characteristic curve of the resistance thermometer has the desired properties, when the thermal coefficient of expansion (TCE), also known as the coefficient of thermal expansion, of the substrate of magnesium titanate lies in the range between 8.5 and 10.5 ppm/K.
In the case of the embodiments of the state of the art, the substrate has always still a very large influence on the characteristic curve, or on the TCR value, i.e. the temperature coefficient of the resistance thermometer. Especially, it is not possible in the state of the art to bring the TCR value of the resistance thermometer into the vicinity of the material of the resistive element as bulk material. Bulk material refers to a state of a material in contrast to the thin film or powder form and means that the material is present in a shape, so that it can be considered as infinitely large in all three dimensions from an atomic point of view. For example, it is, according to the state of the art, practically not possible, to produce platinum measuring resistors with a TCR value in the region above 3900 ppm/K, and yet such values are typical for wound measuring resistors of pure platinum. Furthermore, the shape of the characteristic curve deviates also in the case of resistance thermometers with lower TCR values (typically at 3850 ppm/K) from the shape prescribed according to DIN IEC 751. This has the result, that especially in the case of wider temperature ranges, or in the case of high accuracy requirements, the prescribed tolerance band is departed from. Other negative effects of poor material matching shows up in hysteresis (memory effect) and in poor, long time stability of measured values.